The morphological changes which accompany development of the nervous system have been well characterized. In contrast, the neurochemical and molecular events which underlie these processes are less well understood. We propose to utilize a combination of neuroanatomical and biochemical techniques to elucidate several aspects of the functional role of opioid systems during development of the CNS. The differential developmental appearance of opioid receptor subtypes will be characterized, and will be correlated with the appearance of specific opioid peptide systems. The pharma-ological characteristics of these early receptors will be analyzed and compared to those of the adult. The hypothesis that Mu and Delta receptor subtypes represent intercoverting forms of the same receptor will also be examined in detail. Well characterized behavioral and neuroendocrine deficits have been shown to result from prenatal exposure to morphine. We propose to analyze the molecular basis of these deficits, by comparing several aspects of hypothalamic organization in normal and drug-treated animals. This analysis should provide data relevant to the hypothesis that opioid receptors are important in guidance of neuronal migration.